Within the latest release of the UC Surface v18.104.22.168497 for Windows, the StudioLiveL and StudioLiveR are non-existent.
The Firewire channels for the Digital Return for WDM appear to be mismapped or mislabeled as Aux1 and Aux2. In fact, if you drop the WDM Left to Aux1 and WDM Right to Aux2, they will indeed route to Digital Return from the DAW. Also, I believe that the wording of Aux's to Mix's is unnecessary. They lables should say Mix1 not Aux, especially for the use of this driver within the RM mixer using the CS18ai. Since you have physical lables on the RM's showing the outs as "Mix1, Mix2, etc, you should drop the naming of these in the ASIO drivers and WDM drivers as "Aux1", "Aux2", etc. Shuffling these names in ones head is an unnecessary burden, especially for starting out. The labeling, manuals, videos, etc need to be standardized to use names that match the WDM and ASIO drivers. Let that drive your documentation.